TE and their role in evolution of species 1

Transposable Genetic Material and their role in Evolution of Specie

Submitted by : Nasira Bashir Roll# 1

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CONTENT

• Introduction• Discovery • Properties of TE• Classification of TE• Effect of transposons• Applications of transposons• Role of TE in evolution• Conclusion• References 12/11/2014

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Transposable genetic elements

• They are segments of DNA which are able to “jump” from location to location within a genome. This "jumping" process is called transposition.

• Each transposable element carries transposase gene that encodes for enzyme activity required for its own transposition

TRANSPOSONS Jumping genes Mobile genetic

elements

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These six lab mice illustrate a transposon's ability to affect the genome

schematic diagram of transposition between two prokaryotic plasmids

Transposable genetic elements

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DISCOVERY• The Nobel Prize in Physiology

or Medicine 1983 was awarded to Barbara McClintock "for her discovery of mobile genetic elements".

• She discovered TEs by analyzing genetic stocks of corn that were phenotypically unstable

• The instability involves chromosome breakage and was found to occur at sites where transposable elements were located i.e. at C locus of 9th chromosome.

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Internal structure of maize

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• Genes Studied by McClintock• CI = dominant allele that prevents color from being

expressed in the aleurone layer • C = recessive allele that leads to color development in

the aleurone layer• Bz = dominant allele that produces purple aleurone color • bz = recessive allele that produces a dark brown to

purple-brown aleurone color • Ds = a genetic location where chromosome breakage

occurs

Experiment

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Experiment

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Results of experiment and observations

• Ds requires some factor provided by Ac to move, whereas Ac is independent

• Because of their relationship, Ac is termed an autonomous element and Ds a non-Autonomous element.

• Because both Ac and Ds can move, they are called transposable genetic elements

No autonomous elements

Gene(s)

Autonomous

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• the molecular features of the maize Ac/Ds system are:

• Ac is 4563 bp in length • contain 11-bp inverted

repeats at the ends • 8-bp direct repeats of

target DNA are generated • Ds are truncated versions

of Ac

Results of experiment and observations

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Properties of transposable elements

• Mobility• Considerable diversity. • Transposable elements effectively insert at staggered breaks in

chromosomes. • Major forces in the evolution and rearrangement of genomes • Transposable elements can cause deletions or inversions of

DNA

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Classification of TEs:

Class I (Retrotransposons) Class II (DNA Transposons)• simplest transposons• It transfer through the non-

replicative transposition mechanism

• Doesn’t produce multiple copies

• prokaryotic transposons as well as some eukaryotic transposons

• e.g. Ds and Ac

• complex transposons • It transfer through the

replicative transposition mechanism

• produce multiple copies of the retrotransposon within genome

• Two main types• Viral retrotransposon • Non-viral retrotransposon• majority of eukaryotic

transposons

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Replicative transposition

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Conservative transposition

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Types of Retrotransposons

Viral retrotransposon

• Viral retrotransposons have properties similar to that of retroviruses.

• Ty Transposable Elements can be found within the yeast genome

• The Drosophilacopia transposable element

• There are seven known families of Drosophilacopia transposons within the fruit fly genome

Non-viral retrotransposons• Non-viral retrotransposons

comprise the largest majority of mammalian transposns.

• LINEs. Or long interspersed (transposable) elements

• SINEs, or short interspresed(transposable) elements

• Alu elements are the most common transposable elements within the human genome, making up more than 5%.

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The Effects of TransposonsGene Disorder Transposon

InsertionSite

NFI Neurofibromatosis Intron

F9 Hemophilia B Exon

BRCA2 Breast cancer Exon

CASR Familial hypocalciuric hypercalcemia

Exon

APC Hereditary desmoid disease

Exon

GK Glycerol kinase deficiency Intron

CINH C1 inhibitor deficiency Intron

PBGD Acute intermittent porphyria

Exon

FIX Hemophilia B Exon

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Application of transposable element

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TE in genetic engineering

Bicyclus anynana butterflyBicyclus anynana butterfly which has modified

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Major types of expression and mutagenic cassettes delivered by transposon vectors for versatile applications

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Role of Transposable genetic material in evolution

• McDonald believed that plants and animals were forced to evolve quickly in order to defend their genome against dangerous transposable elements

• McDonald believed that various species had developed two important method of defence.

• Chromatin formation• Methylation

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Transposons and the Evolution of the Immune System

• Geneticist David Schatz and colleagues at Yale University

• 500 million years ago• The RAG transposon is suspected to have emerged

within the genome of human ancestors roughly 450 million years ago.

• The RAG transposon codes for the protein which is responsible for cleaving, recombining, and binding the gene fragments required to synthesize antibody sentinels.

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Britten’s Theory of Evolution

• Biologist Roy Britten of Cal Tech claims that transposition within the genome has had a much more profound impact on evolution than the common single base mutation.

• When a single base mutation occurs, the result is often the production of a slightly altered protein.

• However, when a transposon moves to a new location within a genome, it can alter entire patterns of gene expression, which can drastically effect how an organism develops.

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Transposons in Primate Evolution

• Geneticist Wanda Reynolds believes that Alu elements had an immense influence on the evolution of primates, and humans.

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Future Prospects for Transposons in Research

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References

• http://transposons.tripod.com/id5.html• http://biowiki.ucdavis.edu/Genetics/Unit_II%

3A_Replication,_Maintenance_and_Alteration_of_the_Genetic_Material/9._Transposition_of_DNA/Transposable_Elements

• http://www.ndsu.edu/pubweb/~mcclean/plsc431/transelem/trans1.htm

• http://plato.acadiau.ca/courses/biol/Microbiology/transfer.htm

• https://www.mdc-berlin.de/30144912/en/highlights/archive/2009/highlight5

• http://www.mobilednajournal.com/content/1/1/25

• http://www.eurekalert.org/pub_releases/1998-02/UoG-TEMH-090298.php

• http://www.keystonesymposia.org/14C2

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THANK YOU